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We assessed the transportation tendency of dioxins and predict locations at high risk for dioxin pollution. A new parameter, the compartment distribution coefficient D, was created to account for the tendency of dioxins to preferentially accumulate in particular compartments. It was obtained by a model using levels of polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) in four countries: Japan, the United States, the United Kingdom, and Australia. The comparison with the temporal and spatial variation of D indicated whether the location release or long-range transportation caused the changes. This study showed that PCDD/Fs have the greatest tendency to remain in soil among studied media. A higher D value in Australia may indicate that this location is a potential future reservoir source of dioxins. [ABSTRACT FROM AUTHOR]

• Three different compact city models were designed. • The environmental impact of introducing the compact city models was assessed. • Two different treatments of the withdrawal area in each city model were compared. In this study, first, three compact city models with different degrees of compactness for a prefecture in a large metropolitan area of Japan were designed. Based on the urban classifications "population-induced area," "population-unchanged area," and "withdrawal area," we constructed the compact city models. Next, the impact of introducing the designed compact city models on the summer thermal environment in the 2050s was quantitatively assessed by downscaling simulations from a global scale to an urban scale. Moreover, we examined the effect of a land use change in the withdrawal area on the future thermal environment in the urban area (the population-induced and population-unchanged areas). As expected, a temperature increase in the urban area occurred due to urban densification in the compact city models. On the other hand, the temperature decrease in the urban area as a result of changing the land use of the withdrawal area, i.e., by replacing the withdrawal area with grassland, approximately offset the above-mentioned temperature increase. This implies that, in compact city planning, it is necessary to properly plan not only for the concentrated urban area but also for treatment of the withdrawal area from the viewpoint of environmental impact. [ABSTRACT FROM AUTHOR]

• Gas production performance of field tests in the Nankai Trough was reviewed. • Effect of sand control device plugging on gas production was investigated. • Reasons for the different gas production performance of each well were given. • Proving that reducing pressure drop is an effective way to mitigate sanding. A large number of data on gas production and reservoir characteristics were released after the 2013 and 2017 offshore natural gas hydrate production tests in the Eastern Nankai Trough of Japan. However, the systematic comparison of the two production tests is still limited. Therefore, in this study, we first reviewed the gas and water production processes of the three production boreholes in the two production tests. Some problems were found by comparing the gas and water production rates of each production well and with the existing numerical simulation results. For instance, the gas production rate of well AT1-P3 was extremely low and, distinguished with the previous simulation results, the gas production rates of wells AT1-P and AT1-P3 didn't increase with time. Considering the severe sand production in these two wells, we speculated that the plugging of sand control device (SCD) caused by solid particles deposition was the cause of the above problems. Thus, for the first time, numerical simulation considering the sand production and SCD plugging was performed to evaluate the gas and water production performance of the three production wells. In addition, a preliminary analysis of the production efficiency of each well was carried out. The simulation results showed that a serious plugging occurred at well AT1-P3, which is responsible for its low gas production. In contrast, well AT1-P had a slight plugging, and well AT1-P2 avoided severe sand production owing to the reduced pressure drop, and obtained much higher gas production rate than well AT1-P3 with a lower pressure drop. Furthermore, the simulation results indicated that economically viable gas production is difficult to achieve with current production strategies even if the problems of sand production and SCD plugging are solved. This requires the use of some emerging production technologies in the future. [ABSTRACT FROM AUTHOR]